Fictional donkey (6)
I believe the answer is:
eeyore
'fictional donkey' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for eeyore that I've seen before include "Piglet's sad friend" , "miserable ass" , "Literary donkey" , "Donkey, 19's friend" , "Pooh's pessimistic companion" .)